In laser systems, it can be expensive in terms of cost of acquiring material resources and time for production of the same, to replace certain optical elements such as non-linear optical crystals used for frequency conversion.
For example, a beam of light from a laser source may pass through a beam shaping system (e.g., a lens), and may impinge upon a crystal. In particular, the beam shaping system may focus the beam of light to form a waist, at which may be located the crystal. Typically, the laser system is designed with an expectation of successful performance of the crystal located within the waist of the beam of light. However, should the fluence, that is, the energy per unit area (e.g., Joules per square centimeter), exceed a certain limit for the crystal, the crystal is likely to suffer damage.
When the crystal is originally placed in the path of the laser beam, observation of system success or failure can reveal whether the crystal suffers catastrophic failure, such as bulk fractures. If the crystal is damaged immediately, the laser beam diameter on the crystal may then be enlarged to reduce the fluence on a replacement crystal and thereby reduce the likelihood of immediate damage to the replacement crystal.
However, once a crystal has been operating in the laser system, the laser system might continue to operate regardless of any degree of damage to the crystal until the crystal suffers catastrophic failure such as bulk fractures, at which point replacement of the crystal would undesirably be required. Such replacement of the crystal can entail relatively large expenditure for material, and relatively lengthy downtime (e.g., two, three, or four months of crystal growth time) should a substitute crystal not readily be available.
Thus, a need exists for a system for monitoring the surface of an optical element (e.g., a non-linear crystal in a laser system) to detect damage to the surface prior to catastrophic failure, such as bulk fractures in the optical element. Such system should also be capable of detecting initiation of damage to the surface of the optical element. The system should allow repair of the surface damage so as to permit continued operation of the optical element (e.g., in a laser system).